The purpose of this project is to characterize the blood groups, allotypes, and biochemical polymorphisms of rhesus monkeys (Macaca mulatta) and to use these parameters as markers in immunogenetic and reproductive studies. The controlled breeding program at the University of Wisconsin Regional Primate Research Center makes this colony uniquely suited for such studies. Since one of the missions of the Center is to obtain basic information in reproduction, the immunogenetic parameters will be studied as to their relevance to this area. We have already demonstrated that maternal-fetal incompatibility for blood groups can result in transplacental alloimmunization and we are investigating why the newborn infant does not exhibit hemolytic disease despite the existence of conditions that cause it in humans. Our data from in vivo studies of the clearance of antibody-coated erythrocytes and in vitro phagocytosis of such cells by peripheral blood monocytes strongly suggest that the immunoglobulin class and the amount of antibody on the cell surface play a significant role in the processing of these cells by the monkey's immune system. Finally, we have continued our survey of pregnancy and post-partum serum to determine the frequency of maternal sensitization and the time-course of immune response such as the earliest time that fetal cells can be detected in the maternal circulation and earliest time that circulating antibodies appear. So far we have studied 146 post-partum sera and found about 23% with antibodies. Among the 146 infants born, 16 had antibody demonstrable on their erythrocytes yet none showed any symptoms of hemolytic disease. The 27 alleles in the 13 or more blood group systems and the biochemical polymorphisms (isozymes) which we have described provide a powerful tool for monitoring breeding records, solving disputed parentage cases, measuring inbreeding and calculating gene frequencies for population genetic studies.